Serena back on top of the world

Serena Williams celebrates after claiming the victory which will send her back to the summit on Monday.

Story highlights

Serena Williams will return to the top of the world rankings on Monday

At 31, Williams is the oldest woman to achieve the feat

U.S. star defeated Petra Kvitova in quarterfinals at Doha

Williams to face Maria Sharapova in semifinals

Serena Williams wept with delight after becoming the oldest woman to ever hold the number one world ranking.

The 31-year-old American star clinched a 3-6, 6-3, 7-5 victory over Petra Kvitova in the quarterfinals of the Qatar Open to move back to the summit following a two-and-a-half year interval which almost saw her quit the sport.

"I am so sensitive nowadays -- I am always crying, but I never thought I would be here again you know," Williams told reporters.

"I have been through so much and I never thought I would be here," she repeated.

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It is a remarkable comeback for Williams, who slipped as low as 175 in the rankings after missing almost a year with injury and a life threatening pulmonary embolism in 2011.

But she returned with a bang in 2012, winning Wimbledon, Olympic Gold, the U.S. Open and the WTA Championships, while she has also triumphed in 59 of her past 62 matches.

Williams, who will start her 124th career week at No.1 on Monday, beat Chris Evert's record of 27 years ago when she reached the top at the age of 30 and 11 months -- six months younger than her successor.

The achievement had looked in doubt with Williams 4-1 down in the final set, but the American fought back to clinch a dramatic 7-5 victory.

Williams will now face Maria Sharapova in the semifinal after the Russian defeated Australia's Sam Stosur 6-2 6-4, while Victoria Azaraenka also progressed to the last four after defeating Sara Errani.

The World No.2, who won the tournament in 2005 and 2012, was hoping to bounce back after losing out at the semifinals of the Australian Open.

"I'm very disappointed, I have some regrets about this match," he told reporters.

"He played great and created more chances than I did. He deserved to win. It was a tough loss, but they do happen. Being broken so many times (five) indoors won't get the job done. My game was up and down overall.

"He made it difficult and generated pressure. That made you try to serve harder. When I had some chances I didn't take them. I was maybe a point or two away from taking it into a third set and then the clock resets."